There are a couple of conditions that need to be met in order for your nephew to be able to claim tools. The employer needs to have issued a T2200 (Declaration of Conditions of Employment) and also signed off on an itemized list showing the tools purchased and the costs. The amount claimed is reduced by $1146, and the total deduction cannot exceed $500.
Assuming the conditions are met you can click 'Income' then select 'Employment Expenses.'
http://www.cra-arc.gc.ca/trades/